The disease caused by Mal de Rio Cuarto Virus (MRCV) is a major corn disease in Argentina, accounting for yield losses of greater than 70% in years of severe outbreak (Rodriguez P E et al. (1998) Plant Dis. 82:149-52). The disease is a member of Serogroup 2 of Fijivirus, which includes other viruses such as maize rough dwarf virus, rice black streaked dwarf virus, and pangola stunt virus (Uyeda I & Milne R G (1995) Semin. Virol. 6:85-88). The main vector for MRCV is Delphacodes kuscheli, but other Delphacodes species, such as D. haywardi and D. tigrinus, and Toya propinqua have been shown to carry the virus. The virus does not appear to be transmitted to progeny via seeds. Distéfano at al., Arch. Viral. 147:1699-1709 (2002), analyzed the MRCV sequence and proposed that it is a new Fijivirus species related to MRDV (Maize Rough Dwarf Virus). MRDV is found in several European countries (e.g., the Czech Republic, France, Italy, Norway, Spain, Sweden) and in China, while MRCV has been also detected in Uruguay (Omaghi J. A., Beviacqua J. E., Aguirrezabala D. A., March G. J. and Lenardón S. L. 1999. Detection of Mal de Rio Cuarto virus in Uruguay. Fitopatologia Brasileira 24: 471).
MRCV infection causes abnormal maize development and significantly reduces crop yields. The susceptible phenotype includes stunting, shortening of internodes, multiple ears with scattered grain, deformed tassel with no anthers, presence of small enations in the back of the leaves, reduced roots, cut and reduced leaves. Plants symptoms depend on phenological stage of the plant, plant genotype, and environment (Lenardón et al., “Virus del Mal de Rio Cuarto en maiz”, in Proyecto de Investigaciones en Fitovirologia (Lenardón ed.), 2:10 (1999). Most severe symptoms occur when infected at the coleoptile—first leaf stage.
In the severe MRCV outbreak of 1996-1997, over 300,000 hectares of maize in Argentina were affected, resulting in losses totaling approximately $120 million. Increased populations of Delphacodes kuscheli in 2006 apparently led to a reoccurrence of the viral disease in Argentinean corn plants, which significantly affected the 2007 harvesting. Susceptible genotypes were strongly affected by MRCV at the endemic region (Córdoba Province) and moderately affected at other maize regions.
The development of molecular genetic markers has facilitated mapping and selection of agriculturally important traits in maize, and QTL for resistance to Mal de Rio Cuarto virus in maize have been identified. Microsatellite markers on maize chromosomes 1 and 8 were found to be linked to QTL for resistance to Mal de Rio Cuarto disease (DiRenzo et al. (2004) J. Agricultural Science 142:289-295), and another major QTL conferring resistance of corn to a Fijivirus was identified on chromosome 2 (WO2009/058335). In addition, QTL conferring resistance to Mal de Rio Cuarto Virus in maize were mapped to the short and long arms of chromosome 1, and chromosomes 4, 8, and 10 (Kreff et al. (2006) Journal of Basic and Applied Genetics 17:41-50).
Selection through the use of molecular markers associated with resistance to MRCV infection has the advantage of permitting at least some selection based solely on the genetic composition of the progeny. Moreover, resistance to MRCV infection can be determined very early on in the plant life cycle, even as early as the seed stage. The increased rate of selection that can be obtained through the use of molecular markers associated with the resistance trait means that plant breeding for resistance to MRCV infection can occur more rapidly, thereby generating commercially acceptable resistant plants in a relatively short amount of time. Thus, it is desirable to provide compositions and methods for identifying and selecting maize plants with enhanced resistance to MRCV infection. These plants can be used in breeding programs to generate high-yielding hybrids with resistance to MRCV infection.